Post and tip design for a probe contact

ABSTRACT

The present invention relates to A microfabricated tip and post structure comprising a post having a rough top surface that diffuses incident light and a cross-section, and a tip, lithographically plated on the rough top surface of the post, having a smooth reflective surface appropriate for automatic vision recognition, and having a cross-section that is less than the cross-section of the post.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/194,720, filed Aug. 1, 2005, now U.S. Pat. No. ______.

BACKGROUND

The present invention relates generally to the testing of semiconductorchips, and specifically to the design of probe contactors for suchtesting prior to packaging.

Typically, semiconductor chips are tested to verify that they functionappropriately and reliably. This is often done when the semiconductordevices are still in wafer form, that is, before they are diced from thewafer and packaged. This allows the simultaneous testing of many chipsat a single time, creating considerable advantages in cost and processtime compared to testing individual chips once they are packaged. Ifchips are found to be defective, then when the chips are diced from thewafer, the defective ones can be discarded and only the reliable chipsare packaged. It is an axiom then that the larger a wafer that may bereliably tested at a time, the more savings can be incurred in cost andprocess time.

Generally, when performing wafer testing, a chuck carrying a wafer israised to a probe card to which thousands of probes are electricallycoupled. To test larger wafers, small, high performance probes areneeded. The probes must be able to break through the oxide and debrislayers on the surface of the contact pads of the chips on the wafer inorder to make a reliable electrical contact to each pad. Additionally,the probes must be able to compensate for the fact that the contact padsmay be of different heights (i.e., not all the contact pads on a wafermay reside in the same plane). Furthermore, the chuck and the probe cardmechanical mount may not be precisely parallel and flat, introducingfurther height variations which the probes must accommodate.

Conventionally, cantilever wire probes have been used to test wafers inthis regard. However, cantilever wire probes are too long and difficultto accurately assemble to allow reliable simultaneous contact to all ofthe chips on a conventional wafer. Additionally, cantilever wire probeshave high self and mutual inductance problems which do not make themgood candidates for testing of high-speed devices. These problems areexaggerated when they are used to test larger wafers. Cantilever (orbending) probes can also be fabricated at a small physical scale byvarious microfabrication techniques known in the art. These cantileversprings lack the mechanical energy density (for controlled scrubbing ofthe oxide layer) and spatial efficiency to be ideally effective forreliable testing of large wafers.

A number of attempts have been made to overcome the deficiencies ofcantilever probes, all with varied levels of success. For instance, U.S.Pat. No. 5,98,951, assigned to Form Factor, Inc., describes methods ofproducing spring probes by coating a ductile metal with a spring metal(as seen in FIG. 4). These springs are bending mode springs similar tocantilever springs. Moreover, they are elongated and poorly supported inlateral directions at the contactor causing problems with controlledscrubbing of the contact pads. Furthermore, probes that require a longspring length such as these have relatively poor electrical performance.

U.S. Pat. No. 6,48,638, assigned to Decision Track, describes a torsionspring design, see FIG. 1, which is more mechanically efficient thanother spring designs, and more effective than cantilever designs. U.S.Pat. No. 6,771,084, also assigned to Decision Track, describes thefundamental principle of a single footed torsion spring probe contactor,see FIGS. 2A and 2B. However these designs too, have their limitations.The particular incarnations considered and contemplated by these patentsdo not address or solve many of the practical requirements for a springprobe contactor such as: range of motion, optical characteristicsrequired for vision recognition, practical production means,requirements for high lateral stability of the contact tip in responseto scrubbing forces to name a few.

Improvements in the design of probe contactors have come with advancesin photolithography and associated micromachining techniques. U.S. Pat.No. 5,190,637 to Wisconsin Alumni Research Foundation describes thebasis of multi-layer build up fabrication through lithographicelectro-forming techniques of three-dimensional metal structuresincluding springs and spring contactors. The present applicants havecreated a micro-formed torsion bar probe contactor which overcomes manyof the deficiencies of the prior art and is a subject of the instantapplication.

Another aspect of the present application is the formation of the tip atthe end of the probe. Older pin based contactors, such as cantileverneedle probes or vertically buckling beam probes, are typically builtfrom wire with a sharpened or shaped tip. This type of geometry providesfor adequate electrical contact only if substantial contact force isapplied. High contact force is deleterious to the semiconductor devicesunder test which often include active devices under the I/O pads.Furthermore, pin based contactors cannot be built at the fine pitchesand high pin counts required for modern large wafer test. For these andother reasons, microfabricated probe contactors are an attractivealternative to pin based probe cards.

Microfabricated probe contact tips for use on contactor probes have beenproposed in a variety of configurations and are plentiful in the art. Inmost of these configurations, provision is made for the creation of atip with a well defined and controlled surface shape, size, material,and texture. Each of these elements is important for achieving therequired consistent electrical contact to common IC pad metals such asAl, AlSiCu, Cu, Cu alloys, Au, or solder. Each of these parameters has abearing on the contact performance but control over the geometry isamong the most significant and is a function of the fabricationtechnology employed.

Another factor that is often overlooked is the optical characteristic ofthe tip and adjacent structures. Typically, probe cards are used inconjunction with wafer probers equipped with machine vision systems forautomatic identification of probe tip locations and alignment of thoseto the I/O pads on the wafer, such as that described by U.S. Pat. No.5,321,352, assigned to Tokyo Electron Labs. Basically, a machine visionsystem includes a camera that is positionable and looks at the tips ofthe probe needles. The camera has some magnification appropriate forviewing the geometry of the tip. It also includes a light source such asan LED ring light or a co-axial light. The image from the camera isprocessed by computer so as to determine the location of the tiprelative to the camera's image area. This location information is usedby the prober's computer control algorithm to position thedevice-under-test (DUT) bond pads accurately under the probe tips. Thusthe probe tip must be designed with the vision systems requirements inmind. In particular, vision systems require a good optical contrastbetween the tip and adjacent structures, particularly in the case ofmicrofabricated contactors with small physical dimensions betweenadjacent surfaces. Typical microfabricated spring contactors have smoothplanar surfaces in close proximity to the contact tip surface, creatingdifficulty with regard to the vision recognition systems due toreflections from surfaces other than the tip, as seen in FIG. 5A. Thus,these vision systems often mistake unrelated structures for the tipcausing vision rejections or errors in the captured tip position.

Various attempts to overcome this problem have been suggested, but eachhave had their own problems. For instance, U.S. Pat. No. 6,255,16,assigned to Form Factor, Inc. and shown in FIGS. 3A and 3B, discloses apyramid shaped contactor tip for use with a cantilever probe structure.The pyramid is formed by replicating an anisotropically etched cavity insilicon and bonding the replicated tip to a spring structure. While thistechnique may produce a tip with a good mechanical strength due to itswide base, and the sides of the pyramid reflect light off-axis andappear dark under the normal illumination used for machine visionrecognition, this design has at least two significant drawbacks. Thefabrication sequence is driven by a mold replication technique andrequires a separate bonding step in order to assemble the tip to thespring. This extra bonding step adds significant complexity, yield loss,and cost to the manufacturing process. Furthermore, the pyramid shapeproduces a contact geometry that is limited to a square or rectangularcontact surface which grows in size as it is abraded or re-surfaced asis often done in practical application as a result of abrasive cleaning.Any change in surface shape or size results in a change in contact areaand hence electrical contact characteristics as well as scrub mark.

Another way of solving machine vision problems is to create the tipsignificantly tall (approximately 50 um tall). In this embodiment, thenext underlying planar surface (the post) would be far enough away fromthe focal plane of the vision microscope so that the post surface wouldbe out of focus and only the tip would be in focus. However, this is nota practical solution for tips that are produced by lithographic imagingand electroforming. Such processes have practical limits in aspect ratio(height to width ratio). Furthermore, even if the aspect ratios of ataller tip were practical (typical tips are about the same height as orslightly higher than their smallest dimension which is on the order of 5um to 20 um), a taller tip would be prone to breakage from the lateralscrubbing forces present in use.

Another proposed alternative is to remove part of the post structure,creating a sloped surface around the tip, see FIG. 5B, that cannotreflect illumination back to the vision system. However, a problem withthis design is that it is very difficult to align a tip on the flat topof the now tapered post. Any slight misalignment provides a planarreflective surface near the tip base and causes a bright “crescent” toappear around the tip. The crescent effect interferes with propertip-position recognition causing vision “rejects” or errors in thecaptured visual centroid.

Thus a new design is needed for creating a tip and post structure thatwill resolve the issues of vision errors when a tip is lithographicallyformed on a probe structure.

SUMMARY OF THE INVENTION

Improvements upon the lithography techniques described in U.S. Pat. No.5,190,637 are the subject of U.S. patent application Ser. Nos. 11/01991and 11/102,982, both commonly owned by the present applicant and herebyalso incorporated by reference. Those two applications describe the useof general photolithographic pattern-plating techniques combined withthe use of islands of sacrificial metals to further createmicrostructures such as probe contactors. Using the above techniques,the present applicants have created a micro-formed torsion bar probecontactor which overcomes many of the deficiencies of the prior art andthat is a subject of the instant application.

The present invention is directed to a probe incorporating a torsion baras a spring element and a tip and post structure that resolves currentproblems with automatic vision mechanisms. The torsion bar probe isformed on a substrate which will ultimately hold hundreds or thousandsof probe elements. The probe is connected to the substrate by a foot.Attached to one end of the foot is a trace that electrically connectsthe foot to a via in the substrate, and at the other end of the foot, atorsion bar is attached. At the other end of the torsion bar, a spaceris attached, the spacer being taller than the torsion bar. Atop thespacer, an arm is attached. The arm is more rigid than the torsion bar,meaning that it does not significantly bend to store energy during use.Atop the arm, opposite the spacer, a post (or posts) are attached, andatop the post(s) is a tip, the structure of which will be describedfurther below. A stop is built atop the substrate at a place near andbelow where the spacer and torsion bar are joined. There is a space or agap between the torsion bar and the stop when the probe is in anon-actuated state (i.e., not pressed against a contact pad of asemiconductor device).

In operation, the tip is contacted by an I/O contact pad on a wafer andforced down (in the spatial orientation of the majority of the drawings)towards the substrate. As the tip is pushed down, the arm, which isdesigned to be mostly rigid, tilts causing the torsion bar to twist. Thetorsion bar is firmly affixed to the substrate at the foot end, and issupported both vertically and laterally, but free to rotate, at the stopend. Rotation at the stop end involves a slight motion of the torsionbar (through the gap distance of a few microns) until contact is made tothe stop, after which point the torsion bar pivots against the stop. Theoverall geometry of the probe (including spacer height, arm length, postheight, etc.) dictates the motion in space of the tip as it travelsdownward. The motion is largely in the form of an arc, providing aforward component (in a direction roughly orthogonal to the axis of thetorsion bar) as the tip moves downward. The forward motion of the tipprovides the “scrub” which is necessary in practice to achieve a goodreliable and repeatable contact resistance to the I/O pad.

Utilizing the manufacturing processes described in U.S. patentapplication Ser. Nos. 11/01991 and 11/102,982, the present inventionincludes several novel features not present in the prior art. One of thenovel features of the present invention is that the arm portion is in adifferent planar layer than the torsion bar and may be separated fromthe torsion bar by a spacer. The addition of these two added layersprovides for greater design flexibility towards controlling the path ofmotion of the tip when it is actuated by a largely vertical force whentesting a device. The availability of additional layers of the probe inthis respect is made possible by the new manufacturing processesdescribed in the above patent applications. In fact, as described, thetorsion probe has at least eight planar layers utilized in theconstruction of the torsion contactor spring and these layers afforddesign flexibility to optimize the operational characteristics of thecontactor while accommodating the process limitations imposed bycommercially viable photolithographic micro-electro-forming techniques.The torsion probe may have more or fewer layers than eight withoutdeparting from the spirit of this invention.

The arm of the probe is also made more rigid than the torsion bar sothat it does not act as a spring (as in a cantilever beam spring). Ifthe bar was not rigid, its deformation would increase the scrub lengthbeyond that which may be desired. The arm provides a lever which, inconsort with the stop, transforms the largely linear arc of the tip to anearly pure-torsion rotation of the torsion bar. In another embodiment,the arm is composed of two subarms, one extending from the top of theend of the other. This approach allows a greater clearance between theclosest part of the spring structure and the wafer under test.Additional clearance helps to avoid damage to the wafer from foreignparticles that may become caught between the probe structures and thewafer in the contacted state.

Another novel aspect of the present invention is that a stop is attachedto the substrate and incorporates a lateral support to laterally supportthe torsion bar when it engages the stop. The basic function of the stopis to act as a fulcrum or pivot for the torsion bar. The lateral supportprovides an increase in lateral stability and more control over thetip's scrub pattern.

Another novel aspect of the present invention is the design of the tipand post structure. To ensure that the machine vision systems canaccurately differentiate the tip from the post when both have planarsurfaces, the top portion of the post, to which the tip is coupled, istreated in such a way that it diffuses or absorbs incident light. Thiscan be accomplished several ways, such as through rough plating (such aswith high current plating with or without the addition of grainrefiners) or metallographic decorative etching.

A further refinement is to provide a rough plated skirt that covers notonly the top surface of the support post, but also wraps around the baseof the tip. This construction not only creates a high contrast betweenthe tip surface and the post but also provides for mechanical support ofthe tip in the form of a thickening or gusset around its base. Thegusset further protects the tip from mechanical failure at its basecaused by lateral forces during use, which is particularly useful if thetip has a high aspect ratio (height to width or diameter). This skirtmay also be plated in a pattern that slightly overhangs the poststructure so that slight misalignments (e.g., due to lithography errors)do not result in the exposure of the smooth reflective surface in theshape of a crescent or edge at one side of the perimeter of the post.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5B are examples of embodiments of the prior art.

FIG. 6A illustrates a side view of an embodiment of the presentinvention.

FIG. 6B illustrates a side view of another embodiment of the presentinvention.

FIG. 6C illustrates a side view of another an embodiment of the presentinvention.

FIG. 7A illustrates a perspective view of the embodiment of theinvention shown in FIG. 6B.

FIG. 7B illustrates a perspective view of the embodiment of theinvention shown in FIG. 6C.

FIG. 8 shows a top down view of the embodiment of FIG. 6A.

FIG. 9 shows a view of the embodiment of the invention in FIG. 6A, asseen from the front of the stop element.

FIG. 10 illustrates an embodiment of the stop element of the presentinvention.

FIG. 11 illustrates another embodiment of the stop element of thepresent invention.

FIG. 1 illustrates another embodiment of the stop element of the presentinvention.

FIG. 13A shows a side view of the embodiment of FIG. 6A in an actuatedstate.

FIG. 13B shows a side view of the embodiment of FIG. 6C in an actuatedstate.

FIGS. 14A-14E illustrates the twisting of the torsion bar as anembodiment of the invention is placed in an actuated stated.

FIG. 15 illustrates an embodiment of the tip design of the presentinvention.

FIG. 16 illustrates another embodiment of the tip design of the presentinvention.

FIG. 17A illustrates a perspective view of another embodiment of the tipdesign of the present invention.

FIG. 17B illustrates a cut-away view of the FIG. of 17A.

FIG. 18 illustrates a close-up view of an embodiment of the tip designof the present invention.

DETAILED DESCRIPTION

FIG. 6A shows a probe for testing an electronic device in accordancewith an embodiment of the present invention. This embodiment of theprobe incorporates a substrate 600, a trace layer 610, a footelement.620, a torsion bar 630, a spacer element 640, an arm 650, a post660, a secondary post 670, a tip 680, and a stop element 690. Plated ona substrate 600 is a trace layer 610 providing an electricallyconductive path from the foot 620 to a via 900 (see FIG. 9) in thesubstrate 600. This trace layer 610 may be electroplated gold having anominal height (also termed thickness) of 16 um. The foot 620 providesthe mechanical anchor for the probe. The foot 620 has both a proximalend (the end closest to the via 900) and a distal end (the end furthestfrom the via 900). The foot 620 is connected to a torsion bar 630 at itsdistal end. The torsion bar 630 is the element which provides the probewith its spring like (or compliant) qualities because when it is in anactuated state (i.e., when the probe is contacting an I/O pad of asemiconductor device), the torsion bar 630 will twist as is shown inFIGS. 14A-14E. In one embodiment, the torsion bar 630 is non-axiallyaligned with the foot 620. In one embodiment, the torsion bar 630 is atan angle of about 10 to about 90 degrees relative to the foot 620, butpreferably it is at about a 20 degree angle. This non-axial placementprovides an increased strength in the attachment between the foot 620and the substrate 600, by increasing the moment arm of the attachment,and thereby lessening the peeling forces imparted by the torsion bar 630on the foot/substrate interface during operation. The torsion bar 630 israised off of the substrate 600 so that it is not touching it. At itsdistal end, the torsion bar 630 may have a lateral support element 920(see FIGS. 9 and 10) which will be used in conjunction with the stop 690to prevent lateral displacement of the torsion bar 630 during actuation.

At the distal end (again, the side that is furthest from the via 900)the torsion bar 630 is coupled to a spacer element 640. The spacerelement raises the arm element 650 off from the plane of the torsion bar630. The spacer element 640 provides design flexibility towardscontrolling the path of the motion of the tip 680. It also provides theclearance required between the arm 650 and the substrate 600 toaccommodate a full range of compliance. On top of the spacer 640, is thearm element 650. The arm element 650 is plated generally non-axial tothe torsion bar 630. In one embodiment, the arm 650 is at an angle ofabout 20 to about 160 degrees relative to the torsion bar 630, andpreferably the angle is about 10 degrees. The arm 650 is designed to berigid so that it does not act as a spring. If the arm 650 wereespecially flexible, its deformation would contribute to increasing thescrub beyond the desired limit. In this regard, the arm 650 may be madeof a higher modulus metal (for example, W) than the torsion bar 630(formed from, for example, NiMn), or it may be made shorter, thicker(increasing the height) or wider (or any combination) than the torsionbar 630 as in the preferred embodiment. In this regard, the length,thickness, and width can be expressed in the three axes ofthree-dimensional Cartesian coordinates, conventionally denoted the x,y, and z axis. The x-axis represents the length, the y-axis representsthe width, and the z-axis represents the thickness.

The fact that the arm 650 is on a different plane than the torsion bar630 is a novel feature of the present invention. This feature is madepossible by the use of the photolithography process described in U.S.application Ser. Nos. 11/01991 and 11/102982, which are incorporatedherein by reference.

Atop the distal end of the arm 650, a first post 660 is plated. Thefirst post element 660 also provides design flexibility in controllingthe path of the motion of the tip 680 during actuation. The first post660 may have a tip 680 plated on top of it, or there may be a second (ormore) post element(s) 670, optionally having a smaller surface area thanthe first post element 660, plated between the first post 660 and thetip 680. The post element (either a first post 660 or combined with thesecondary post element 670) extends the tip 680 vertically away from thearm 650 allowing the full target deflection of the tip. The secondarypost 670 may be added to the first post 660 to allow proper geometriesfor tip scrub while maintaining manufacturability. The first post 660may be plated large enough to allow lithography and plating with aroughly (or slightly larger) 1:1 aspect ratio (width to height). Thesecondary post 670 is ideally smaller in order to more adequatelyaccommodate a proper scrub. A smaller secondary post 670 alsoaccommodates lithographic alignment errors between the two post layers.

The tip 680 does not need to be concentric with whichever post (660 or670) it is plated on. It may be advantageous to plate the tip 680 offsetfrom the center of the post (660 or 670) upon which it is plated inorder to eliminate any interference the post (660 or 670) may have withthe device under test due to the deflection angle. The tip 680 may becircular, rectangular, blade-shaped, oval, teardrop shaped, or any othershape that can be formed lithographically.

Underneath the arm 630 is a stop element 690. The stop element 690 isplated on the substrate 600 and there is a gap 910 (see FIG. 9 and 10)between the arm 630 and the stop 690. The gap 910 may be formed byplating approximately 1 um to approximately 20 um of sacrificial copperbetween the stop 690 and the torsion bar 630 during manufacture, andpreferably about 6 um of sacrificial copper is plated. The sacrificialmetal will then be removed in the final stages of production of theprobe. The stop 690 is designed to provide vertical and lateral supportto the torsion bar 630 when the probe is in an actuated state. The basicfunction of the stop 690 is to act as a fulcrum or pivot for the torsionbar 630. In one implementation, the stop 690 is partially “buried” underthe torsion bar 630 in a shallow pocket formed by the lateral supportelement 920 of the torsion bar 630 (see FIGS. 9 and 10). In anotherembodiment, the stop 690 is completely placed under the distal end ofthe torsion bar 630 (see FIG. 11). In the latter embodiment, the stop690 may also incorporate a lateral support element 1100 and the torsionbar 630 may incorporate two lateral support elements 920 on either sideof the stop lateral support element 1100. This embodiment laterallysupports the torsion bar 630 in both the positive and negative xdirections, providing better lateral stability and scrub mark positionaccuracy. FIG. 1 also shows another embodiment of the stop element 690.In this embodiment, the torsion bar 630 has one lateral support element920 and the stop 690 has two lateral support elements 1100 on eitherside. Other stop configurations providing a pivot while constraininglateral motion may be implemented without departing from the spirit ofthis invention.

FIG. 6B depicts an alternative embodiment of the present invention. Inthis alternative embodiment, a second trace layer 695 (which may beconnected to trace layer 610) is also plated underneath the stop 690.The purpose of this second trace layer 695 is so that the stop layer 690can be plated in the same plane as the foot 620. This feature alsoreduces the thickness of the spacer element 640

FIG. 6C depicts an alternative embodiment of the present invention. Thisalternative embodiment is substantially the same as FIG. 6B but shows aprobe element with a first arm 650 attached to the torsion bar 630 and asecond arm 655 that sits at the distal end of the first arm 650. Becauseof the dual arm structure, a spacer 640 is not necessary. The dual-armfeature allows for greater clearance between the closest part of theprobe structure and the wafer under test. Additional clearance can helpavoid damage to the wafer surface from foreign particles caught betweenthe probe structure and the wafer surface in the actuated state. This isgraphically shown in FIGS. 13A and 13B. FIG. 13A shows an embodimentlike that in FIG. 6A or 6B. In one embodiment, the proximal end of thearm 650 (the end furthest from the tip 680) may be less than 20 um fromthe wafer under test 1300. In FIG. 13B, the lowest part of the secondarm 655 may be roughly 45 um from the wafer under test 1300 and thelowest part of the arm 650 may be roughly 56 um from the wafer undertest 1300. In both FIGS. 13A and 13B, it is assumed that the probestructure traveled 100 um which is the distance between the substrate600 and the lowest part of the arm (or first arm) 650.

One could increase the height of the posts 660, 670 in order to creategreater clearance between the wafer surface and the probe structure, butthis is undesirable because it increases scrub length and adds processcomplexity and cost. While the embodiment shown in FIG. 6C shows a dualarm structure, a probe may be constructed with many more arms withoutparting from the spirit of the present invention. It is also possible toreplace the post with a short arm (the difference being that a post hasroughly equal length and width or may be round while an arm issubstantially longer than it is wide).

FIG. 7A depicts the embodiment of FIG. 6A from an angle which shows thenon-axial alignment of the torsion bar 630 to the foot 620, and thenon-axial alignment of the arm 650 to the torsion bar 630.

FIG. 7B depicts the embodiment of FIG. 6C from an angle which shows thenon-axial alignment of the torsion bar 630 to the foot 620, and thenon-axial alignment of the arms 650 and 655 to the torsion bar 630.

FIG. 8 shows a top down view of the embodiment of the present inventionshown in FIG. 6A.

FIG. 9 is a perspective view of FIG. of 6A. It is the view of FIG. 6Aone would see if he was looking straight-on at the stop 690 with thetorsion bar 630 being behind the stop 690.

In an embodiment of the present invention shown in FIG. 6A the tracelayer 610 may be a layer of Ni or NiMn plated 25 um high which in turnmay also be plated on a conductive base layer that may be 2000 A Crunder 5000 A of Au under 15 um of electroplated Au. The stop 690 maybe alayer of Ni or NiMn plated to a height of 28 um, and the foot 620 may beplated in two sections: one plated at the same time as the stop 690, theother plated at the same time as the torsion bar 630. Overall, the foot620 may be a layer of Ni or NiMn (or a combination of both) plated to aheight of 67 um. The torsion bar 630 may consist of NiMn that is 39 umhigh. It should be understood that this is the thickness (in height) ofthe torsion bar 630, not the height of the torsion bar from the plane ofthe substrate 600. The torsion bar 630 may also be 40 um in thicknessand 804 um in length. NiMn is a useful alloy for the creation of thetorsion bar 630 because of its spring like qualities. The arm 650 may beNiMn or Ni plated to a height of 60 um, a width of 55 um and a length of473 um. The first post 660 may be Ni or NiMn plated to a height of 68 umand the second post 670 maybe be Ni or NiMn plated to 28 um. The tip 680may be PdCo or Rh plated to a thickness of 11 um or it may be acombination of Ni or NiMn and RdCo or Rh totaling 11 um in thickness.

In the embodiment of the FIG. of 6A, there may be a distance of 100 umfrom the top plane of the arm 650 and the top plane of the tip 680.There may also be a distance of 110 um between the top plane of thesubstrate 600 and the bottom plane of the arm 650. The total distancefrom the top plane of the tip 680 and the top plane of the substrate 600may be 270 um.

In the embodiment of FIG. 6C, the distance between the top plane of thefirst arm 650 and the top plane of the tip 680 may be 148 um and thedistance between the top plane of the second arm 655 and the top planeof the tip 680 may be 93 um. The distance between the top plane of thesubstrate 600 and the bottom plane of the second arm 655 may be 15 um.

While the forgoing dimensions give approximate dimensions for exemplaryembodiments of the present invention, the actual dimensions may bevaried by as much as ten times without significantly altering the designprinciples utilized. While Ni is utilized to make a majority of theprobe element in the above examples, many other metals and metal alloyssuch as NiMn, Tungsten Alloys, and Cobalt alloys may also be used. Ingeneral, it is desirable to use metals that can be electroformed andthat provide good mechanical strength, toughness and thermal stability.

The substrate 600 may be any type of substrate, including semiconductormaterials such as silicon, germanium and gallium arsenide, ceramics suchas alumina, aluminum nitride, glass bonded ceramics, low temperaturecofired ceramics (LTCC) and high temperature cofired ceramics (HTCC),dielectric coated metals or glasses. The substrate 100 is preferably aLow Temperature Co-fired Ceramic (LTCC) substrate with built in vias 900such that electricity may be conducted from one face 600 a of thesubstrate 600 to the other face 600 b of the substrate 600 by way of thevias 900. In an embodiment of the present invention, the vias 900 aremade from gold, but any other conductor such as copper, tungsten orplatinum may be used. The ceramic may also contain electricalredistribution conductors, making it an electrical wiring board or“space transformer” as is commonly known in the art.

Another novel feature of the present invention is the design of the tipand post structures on the probe. The quality and reliability of theelectrical contact to a semiconductor I/O pad is a function of the tipmaterial, tip size, tip geometry, scrub motion, and contact force. Eachof these parameters has a bearing on the contact performance, but tipgeometry is among the most significant and is a function of thefabrication technology employed. Older contactors, such as cantileverneedle probes or vertical buckling beam probes were typically built fromwire with a sharpened or shaped tip. However, this type of tip geometryis difficult to control at the micron scale and requires high contactforce which is deleterious to the semiconductor devices under test.Furthermore, pin based contactors cannot be built at the fine pitchesand high pin counts required for modern wafer test. For these and otherreasons, microfabricated probe contactors are an attractive alternative.New microfabricated spring contactors often have smooth planar surfacesin close proximity to the contact surface which creates difficulty forautomatic vision systems to easily identify the tip due to reflectionsfrom surfaces other than the tip. The new post and tip designs of thepresent invention overcome this common problem.

FIG. 15 shows one embodiment of the tip and post design of the presentinvention. In FIG. 15, the bottom (in the view shown) of the post 670has a roughened surface 1500. The surface is roughened prior tolithographically pattern-plating the tip 680 on the post 670, and so thetip 680 is plated directly on the roughened surface 1500. The roughenedsurface 1500 can be formed by plating metals and alloys such as Ni, Nialloys such as NiMn, NiCo, NiW, or NiFe, W alloys such as CoW, Cr orsimilar metals at a high current, or by the addition of grain refinersor other additives such as Mn salt in a Ni Sufamate bath, or in anyother manner known in the art of electroplating and electroforming tocreate a roughened surface. As shown in FIG. 18 (not drawn to scale),the roughened surface 1500 may have peaks 1510 and valleys 1520 and apeak 1510 may rise up approximately 0.1 um to approximately 5 um from avalley 1520, and preferably the height is approximately 1 um from peak1510 to valley 1520. The arrows in FIG. 15 denote light (the solid linesindicate intense light, the dashed lines indicate diffused, diffracted,absorbed, or in some other way, less intense light). Thus, FIG. 15 showsthat the light reflected back from the roughened surface 1500 isdiffused and scattered. This helps the automatic vision systems toresolve the tip 680 more clearly by providing greatly improved contrastbetween the tip and the post surface(s).

A further refinement to this idea is depicted in FIG. 16. In FIG. 16, arough plated skirt 1720 is plated on the bottom portion of the post 670and also around the base of the tip 680. This construction creates ahigh contrast between the surface of the tip 680 and the post 670 andalso provides for mechanical support of the tip 680 in the form of athickening or gusset around the base of the tip 680. The gusset furtherprotects the tip 680 from mechanical failure at its base caused bylateral forces during use, particularly if the tip 680 has a high aspectratio (height to width or diameter).

FIGS. 17A and 17B depict another embodiment of the tip and post designof the present invention. In FIGS. 17A and B a roughened metal is platedin a cap 1710, 1700 over the posts 670, 660 so that the metal overhangsthe post structures. This fabrication method insures that slightmisalignments (due to lithography errors) do not result in the exposureof the smooth reflective surfaces of the posts 660, 670 which couldcause a crescent or edge at one side of the perimeter of the posts 660,670.

While the description above refers to particular embodiments of thepresent invention, it should be readily apparent to people of ordinaryskill in the art that a number of modifications may be made withoutdeparting from the spirit thereof. The accompanying claims are intendedto cover such modifications as would fall within the true spirit andscope of the invention. The presently disclosed embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than the foregoing description. All changes that comewithin the meaning of and range of equivalency of the claims areintended to be embraced therein.

1. A microfabricated structure, comprising: a post having a rough topsurface with a surface area and the top surface having a property ofdiffusing, diffracting, or absorbing incident light; and a tip,lithographically pattern-plated on the rough top surface of the post,having a smooth reflective surface suitable for machine recognitionsystems, and having a contact surface area that is less than the surfacearea of the top surface of the post.
 2. The microfabricated structure ofclaim 1, wherein the top surface includes metal plated at a highcurrent.
 3. The microfabricated structure of claim 1, wherein the topsurface is etched to a rough finish.
 4. The microfabricated tip and poststructure of claim 1, wherein the top surface is metal plated with atleast one additive to provide roughness.
 5. The microfabricatedstructure of claim 2, wherein the metal is one of Ni, NiCo, NiW, NiFe,CoW, Cr, or NiMn.
 6. The microfabricated structure of claim 4, whereinthe at least one additive is Mn salt in a Ni Sufamate bath.
 7. Themicrofabricated structure of claim 5, wherein the at least one additiveis a grain refiner.
 8. The microfabricated structure of claim 1, whereinthe tip is non-centered on the post.
 9. The microfabricated structure ofclaim 1, wherein the post is approximately 28 um in height.
 10. Themicrofabricated structure of claim 1, wherein the tip is composed ofeither PdCo or Rh.
 11. The microfabricated structure of claim 1, whereinthe tip is approximately 11 um in height. 12-18. (canceled)
 19. Amicrofabricated structure, comprising: a post having a top surface withan area; a tip having side walls and a top surface, said top surfacehaving a smooth reflective surface appropriate for machine visionrecognition of tip position and size, said tip being plated on the topsurface of the post, and having an area less than the area of the topsurface of the post such that once plated on the top surface, the topsurface has an exposed portion and an unexposed portion; and a skirtplated over the exposed portion of the top surface of the post and overat least a portion of the side walls of the tip, said skirt having aproperty of at least one of diffusing, diffracting or absorbing light.20. The microfabricated structure of claim 19, wherein the skirtprovides mechanical support to the tip.
 21. The microfabricatedstructure of claim 19, wherein the skirt overhangs the top surface ofthe post.
 22. The microfabricated structure of claim 19, wherein theskirt includes metal plated at high current.
 23. The microfabricatedstructure of claim 22, wherein the metal is one of Ni, NiMn, NiCo, NiW,NiFe, CoW, or Cr.
 24. The microfabricated structure of claim 19, whereinthe skirt includes at least one additive.
 25. The microfabricatedstructure of claim 24, wherein the additive includes a Mn salt in a bathof Ni Sufamate. 26-32. (canceled)
 33. A microfabricated structurecomprising a tip lithographically pattern-plated on a post, wherein thetip has a smooth surface suitable for automatic vision recognition andthe post has a surface that has at least one property that aids anautomatic vision recognition system in identifying the tip.
 34. Themicrofabricated structure of claim 33 wherein the property is one ofdiffusing, diffracting, or absorbing light.
 35. The microfabricatedstructure of claim 1, wherein the top surface has at least one peak andat least one valley.
 36. The microfabricated structure of claim 35,wherein the at least one peak rises between approximately 0.1 um and 5um above the at least one valley.
 37. The microfabricated structure ofclaim 36, wherein the at least one peak rises approximately 1 um abovethe at least one valley.
 38. The microfabricated structure of claim 19,wherein the skirt has at least one peak and at least one valley.
 39. Themicrofabricated structure of claim 38, wherein the at least one peakrises between approximately 0.1 um and 5 um above the at least onevalley.
 40. The microfabricated structure of claim 39, wherein the atleast one peak rises approximately 1 um above the at least one valley.